The manufacture of footwear, particularly more rugged footwear such as winter boots, work boots and athletic shoes, represents an ongoing balance between weight and durability. To reduce weight and to cut costs therein, it has become common to use lighter weight foamed or expanded plastics materials in the production of such footwear. For example, blown polyurethane has become commonly used as a mid-sole material for winter boots and athletic shoes. It is not only lighter than other plastics or synthetic rubbers (e.g. polyethylene) previously used, but exhibits good thermal insulative properties.
As a general rule, however, such lighter plastics materials are less durable, which makes them unsuitable for applications, such as lower soles, involving contact with the ground or other ambient surroundings. For children's footwear, this is not as significant a problem, as children are lighter, resulting in less wear of the item of footwear. Children's footwear also frequently require replacement of the footwear due to growth, which tends to be as rapid, if not more, than the need to replace the footwear due to wear. However, for adults, who are no longer growing, replacement is driven primarily by wear.
EVA (Ethylene Vinyl Acetate) is another inexpensive, lightweight plastics material with good insulation properties that is often used to form the insole or midsole of footwear, such as winter boots. However, EVA is also not very wear-resistant and, as such, has not been applied to forming portions of such footwear designed to be in contact with the ground, as the footwear will become unwearable due to abrasion quite rapidly. EVA has been used to make footwear for small children, as their light weight reduces the wear, and their rapid growth means the item of footwear will need to be replaced in a larger size before becoming too worn to wear.
It is an object of this invention to partially or completely fulfill one or more of the above-mentioned needs by providing an item of footwear that is not only cost-effective to mass manufacture, but which is also lightweight and resistant to undue wear through abrasion, whilst at the same time offering good thermal insulative properties.